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Phase stabilization principle and precipitate-host lattice influences for Al-Mg-Si-Cu alloy precipitates

Abstract

In this work, we seek to elucidate a common stabilization principle for the metastable and equilibrium phases of the Al–Mg–Si–Cu alloy system, through combined experimental and theoretical studies. We examine the structurally known well-ordered Al–Mg–Si–Cu alloy metastable precipitates along with experimentally observed disordered phases, using high angle annular dark field scanning transmission electron microscopy. A small set of local geometries is found to fully explain all structures. Density functional theory based calculations have been carried out on a larger set of structures, all fully constructed by the same local geometries. The results reveal that experimentally reported and hypothetical Cu-free phases from the set are practically indistinguishable with regard to formation enthalpy and composition. This strongly supports a connection of the geometries with a bulk phase stabilization principle. We relate our findings to the Si network substructure commonly observed in all Mg–Al–Si(–Cu) metastable precipitates, showing how this structure can be regarded as a direct consequence of the local geometries. Further, our proposed phase stabilization principle clearly rests on the importance of metal-Si interactions. Close links to the Al–Mg–Si precipitation sequence are proposed.

Category

Academic article

Client

  • Research Council of Norway (RCN) / 205353
  • Notur/NorStore / NN8068K

Language

English

Author(s)

Affiliation

  • Norwegian University of Science and Technology
  • SINTEF Industry / Materials and Nanotechnology
  • University of Rouen Normandy
  • Germany

Year

2014

Published in

Journal of Materials Science

ISSN

0022-2461

Volume

49

Issue

18

Page(s)

6413 - 6426

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